Unit 12 Notes

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Motion Forces
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What is a Force?

• FORCE Any push or pull which causes something
  to move or change its speed or direction

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What is a Force?

• Forces can be BALANCED or UNBALANCED
• Balanced forces are equal in size and opposite in
  direction
• Unbalanced forces are not equal in size and/or
  opposite in direction. If the forces on an
  object are UNBALANCED, we say a NET force
  results.

Amusement Park Forces
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What is a Force?

• Can you think of examples of forces?
• Balanced Forces?
• Unbalanced Forces?

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What is Gravity?

• GRAVITY An attraction force between all masses
• Newtons universal law of gravitation Every
  object in the universe exerts a gravitational
  attraction to all other objects in the universe
• The amount of gravitational force depends upon
  the mass of the objects and the distance between
  the objects

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What is Gravity?

• The greater the mass, the greater the force
• The greater the distance, the less the force
• Acceleration due to gravity 9.8 m/s2

Gravity in Space
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• Weight is a measure of the gravitational force
  between two objects
• The greater the mass the greater the force
  (weight)
• Measured in units called Newtons (N)

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• Weightlessness free from the effects of gravity

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Gravity by Brainpop

• ) How does the gravity on the moon compare to the
  gravity on Earth?
• ) Why dont you notice your own gravitational
  pull on the Earth?
• ) On what two things does the force of gravity
  depend?

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What is Friction?

• Friction A force that opposes or slows down
  motion
• Caused by the physical contact between moving
  surfaces
• The amount of friction depends upon the kinds of
  surfaces and the force pressing the surfaces
  together
• Changes motion into heat

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Sliding Friction

• Occurs when two flat solid surfaces slide over
  one another.
• The surfaces come into contact with one another.
• Hardest type of friction to overcome.
• If the surface was oily it might become more easy
  to resist.

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Rolling Friction

• Occurs when a round object rolls on a flat
  surface.
• Easier to resist friction, because not all of the
  surface is touching the ground.

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Air/Fluid Friction

• Air/Fluid Friction The force of air/fluid
  exerted on a falling object
• The air/fluid pushes up as gravity pulls down
• Dependent upon the shape and surface area of the
  object
• When the air/fluid resistance equals the force of
  gravity, terminal velocity is reached
• Terminal velocity is the highest velocity that an
  object will reach as it falls

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What is Friction?

• What are some ways athletes uses friction?

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Newton's Laws of Motion
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Newton's Laws of Motion

• First Law An object at rest stays at rest or an
  object in motion, stays in motion (in the same
  direction/at the same speed) unless acted upon by
  an unbalanced force
• Also called the law of inertia.

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• Inertia
• A property of matter
• The tendency of an object to resist any change in
  its motion
• The greater the mass the greater the inertia
• The greater the speed the greater the inertia

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Examples of Newtons 1st Law
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Example of Newtons 1st Law
Newtons third law Inertia wants to resist
change in motion." Some of the funniest things
in cartoons follow physics , but simply
exaggerated or just plain ignored this law. Wyle
Coyote hangs suspended in air over that canyon
for a lot longer than an object would in reality,
but it is the anticipation of the drop and Wyle's
facial recognition of the upcoming pain that is
so classically cartoonish. So some laws are
stretched for comical effect.
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Newton's Laws of Motion

• Second law The greater the force applied to an
  object, the more the object will accelerate. It
  takes more force to accelerate an object with a
  lot of mass than to accelerate something with
  very little mass.

The player in black had more acceleration thus he
hit with a greater amount of force
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Newton's Laws of Motion

• Second law
• The greater the force, the greater the
  acceleration
• The greater the mass, the greater the force
  needed for the same acceleration
• Calculated by F ma
• (F force, m mass, a acceleration)

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Examples of Newtons 2nd Law
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Examples of Newtons 2nd Law
The second law states that unbalanced forces
cause objects to accelerate with an acceleration
which is directly proportional to the net force
and inversely proportional to the mass. This one
is telling us that big heavy objects dont move
as fast or as easily as smaller lighter objects.
It takes more to slow down a charging bull then
to slow down a charging mouse. http//www.youtub
e.com/watch?vGEzyNNhOeBw
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Newton's Laws of Motion

• third law For every action force, there is an
  equal and opposite reaction force. (Forces are
  always paired)
• http//www.youtube.com/watch?vshfOQ94AHag

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Examples of Newtons 3rd Law

• rockets leaving earth
• guns being fired
• c) jumping out of a boat onto the dock

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Examples of Newtons 3rd Law
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• Momentum The quantity of motion
• A property of moving objects
• Calculated by P mv
• (p momentum, m mass, v velocity)
• Law of conservation of momentum the total
  amount of momentum of a group of objects does not
  change unless outside forces act on the objects

Rollercoaster Momentum
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Newtons Laws by Brainpop

• ) Why does a ball roll across a rug and come to a
  stop?
• ) What is a net force?
• ) Give an example of Newtons 3rd Law